Tailoring the Pt/ionomer interface for enhancing the local oxygen transport in proton exchange membrane fuel cells

Abstract

In order to realize the high-power operation of low-cost proton exchange membrane fuel cells, it is urgent to solve the problem of oxygen mass transfer in a low Pt loading cathode at high current density. More exactly, the high local oxygen transport resistance (R_ionomer) originating from the dense ionomer film on the Pt surface results in significant voltage losses. Herein, this paper proposes an exceptionally simple and cost-effective strategy to precisely regulate a Pt/ionomer interface to decrease R_ionomer only by introducing hydrophobic nano-SiO₂ into a cathode catalyst layer. As a result, the cathode catalyst layer modified by nano-SiO₂ with a particle size of 10 nm and a content of 10% exhibits optimal mass transfer characteristics, and a specific Pt/ionomer interface with low R_ionomer is established. The microstructure characterization of the catalyst layer confirms that the majority of ionomer adheres to nano-SiO₂ particles and evenly distributes around the Pt/C agglomerates. Moreover, the stronger affinity of nano-SiO₂ to ionomer is verified by molecular dynamics simulation. Collectively, the ability of nano-SiO₂ to capture ionomer effectively reduces the ionomer density on the Pt surface, thus establishing a highly efficient oxygen-delivering Pt/ionomer interface. This work highlights an extremely promising method for Pt/ionomer interface construction of catalyst layer with high oxygen mass-transfer characteristics.